The invention relates generally to a process for electrically insulatingly enclosing a junction between electrically conductive elements, and a material for use in carrying out such a process.
In one form of process for producing an electrically insulating sheathing around the junction between electrically conductive elements such as wires, an electrically insulating sheathing material is arranged around the junction by means of an ultrasound welding operation, thereby to cover the junction. As indicated, the electrically conductive elements which are joined together and then sheathed in that manner may be for example wires in electrical equipment, which are connected together for example by means of an ultrasound welding apparatus. In order to join the electrically conductive elements, it is first necessary to strip the insulation from those elements at the location at which the elements are to be joined together. The elements are then welded together along the location at which they are to be connected, for example by means of the ultrasound welding apparatus referred to above. After the ultrasound welding operation has been carried out, then electrical insulation around the junction must be restored in order not to leave electrically live components exposed. The electrically insulating sheathing around the junction must not only have a certain level of dielectric strength and a given specific resistance, but it must also be resistant to temperature and furthermore it must be satisfactorily sealed. The sealed nature of the sheathing around the junction between the electrically conductive elements is necessary in order to afford protection against the ingress of moisture which would have an adverse effect on the junction between the electrically conductive elements, that is to say, it would increase the contact or transfer resistance, due to the resulting corrosion or oxidation caused by the moisture which penetrated into the junction. One form of the process for electrically insulating enclosing a junction between electrically conductive elements provides that a self-adhesive strip of insulating material is wound around the junction. However, it will be appreciated that the operation of winding the strip of insulating material around the junction takes up a relatively large amount of time, with the result of high labor costs. In another form of such a process for electrically insulatingly enclosing a junction between electrically conductive elements, a plastic material is injected around the junction. That operation requires an injection molding tool which must be arranged around the junction to be enclosed. The sheathing of plastic material which is injected around the junction in that way is of relatively large wall thickness in order to ensure that the sheathing has the necessary electrical properties. However, because of the relatively large wall thickness of the sheathing injected around the junction, in which respect the material used may be for example polyvinyl chloride, such a sheathing suffers from the disadvantage that problems may be encountered when the joined electrically conductive elements have to be inserted into a duct. Another process for producing an electrically insulating sheathing around a junction between electrically conductive elements involves using a shrink tube which is caused to shrink around the junction by virtue of heat being appropriately applied to the tube. However, such a sheathing configuration suffers from the disadvantage that it is not possible completely to avoid cavities being formed between the electrically insulating sheathing and the junction between the electrically conductive elements, so that the junction is not reliably protected from the effects of corrosion and oxidation. The same difficulties are also encountered when using another form of process for producing an electrically insulating sheathing around a junction between electrically conductive elements, which involves arranging an insulating film or foil around the junction, being fixed in position by means of an ultrasound welding operation. That process also does not make it possible to reliably avoid the formation of cavities between the electrically conductive elements and the electrically insulating sheathing with the result that moisture can penetrate into such cavities and thus give rise to corrosion and oxidation, with the above-indicated detrimental consequences. Thus, such chemical changes at the junction as are caused by corrosion and oxidation phenomena can cause the contact resistance of the junction between the elements to reach unacceptable high levels.